Polyolefin based microporous membranes are used as separators for lithium ion batteries. They offer thin and uniform structures along with small pore size and good shutdown feature, but are limited on high temperature stability, which leads to loss of structural integrity, if the battery is abused and sees higher temperatures There is a need for a separator that offers thin, uniform structures, small pore size and still offer good shutdown along with high temperature stability to improve the safety of lithium ion batteries.
The composite separator of the current invention offers a solution to this need with thin, uniform structures, small pore size, higher mechanical properties required to make good cells with a separator. It also offers good shutdown properties and maintains its structural integrity at very high temperature. This property does not allow the direct contact between the positive and negative electrodes at higher temperatures at thus helps in improving the safety of lithium ion batteries.